Most of my trips were in groups of 4 or more. I've tripped with just one other person, on the same psychedelic, only once (mdma is a different story).
As for one-on-one, I'll just put it bluntly; though we (myself and someone I was seeing at the time) bonded through being on the same substance, it didn't bring us that much closer. We've done other things like go out to dinner, go out with friends at a myriad of places or just sitting around someplace comfortable and just talking, which was more intense. It's not that psychedelics were marginalized in my mind (especially at the time). But it probably was to my partner. We just liked spending time together, and I'm aware that she didn't really care what we did. It didn't help that it was my suggestion, because she was (and probably still is, though I don't talk to her anymore) a very strong-minded person. We used lsd, and though it was cool as hell frying with her in a hotel room for a day, we've had better times than that. Not to mention that it was her first time, so I had to constantly answer all the questions she had during the experience. She was just in awe and wonder at the feelings and visuals, so I was more like a sitter. Still, that day was one of my best days with lsd, even though she didn't care much about it. It was also a spur of the moment thing, which isn't the best way to go about a bonding experience imo and ime.
My current SO does not like psychedelics. She's seen a few of my bad lsd trips, so without her saying so I could tell she's thinking "fuck that." Which, btw, neither of us count mdma+weed as a true psychedelic experience, even though it arguably is and she had done that a lot back then. (She's scared of my DOPr, which I find hilarious.
) But she had already been into that "scene" from her ex best friend's influence, so it started with her. That one, yeah, we bonded a lot during that time.
I've never had the chance to try this with a girl I was seeing, that had a natural interest in actual psychedelics. Platonic friendships with girls, yes, but honestly the experience is just really similar to tripping with my guy friends, so not much bonding was achieved. Thankfully.
I'd think that unless both are really open to it, make it a special occasion to trip on a psych, and really connect emotionally outside and inside the trip, then it could be a grand experience for sure. I think it's kind of rare though, since not many girls do psychedelics to bond one-on-one. At least not the ones I ever knew.
That's what mdma is for though. If you consider it a psychedelic (I don't, even though it technically is one), you'd probably have had more answers by now.
